Screw tap



932. H. STEINRUCK 1,874,378

scm 'm Filed Feb. '1, -1929 li elentd 30, 1 932 0H. "Wit" de ineation filed llelereery 7, 182$, fieriel l'io. 33%,243, axle ire liermszzgr l ehreory 11, 1823;

ll e, thread is to be reduced within the leier of the bore WllillOllt play between e lemele and male enge "ing SCI'GWSylJllQH hecessery in the case 0% tapping their the "iginel hore hole should be smaller than lhe L oreuicel core dimension This is H8665" for example, with most pipe connecwherein the are frequently only A rep which is made with the sol; flenlediemeter else at; the iniizielly rig end would not engege Ell ell. in the eii'ieller acres, Such taps ere t erefore cl ricer me lip (so llie form; er? ep so thee-she hole roughed one eme time the ceiling; of the ierrever gives disedveiiiegeously lerge o shavings which eesily leer cut c of the ihieed-peelrs is the here. Sluice es hored smaller than the core dimension also he provided with threads by cursing irst of all with e screw he-p, the ccre r of which is smeller then the exist- 3 core diameter of the horehele, The och r nest seed illi the larger core diemeloer n engeges reedily in the roughmm. groove .d deals with the remeiniiig; e .lcriel er, izhe {Lop screrwihreed ore. This cells, however, for

clues b ouhles the time of opereiioeo s in which the screw tsp may he e is certainly possihle e0 errerige rew taps one hehind 'lJhe ether coir Working time cl such. e stepped L ly rather l uriherreere it cancel he employed when she depth, she i c hole does moi; e-llcw of she rep reusing; ough ilie eri'nicle in which the screw thread oeing'cut.

According to she present inventions smell er edvence cuiter is combined. with e; nermelly lergescrew tap in such a, fashion hhel;

me teeth belonging to the smaller advance fir v v first precede alone for a short distance 1 v i 1 ierri to form as so-celied shepperl c ew teeth enter 1' suited to the conditions and just so much. that they en age with certainty well in the smaller here he e; next follow together in free order smell end normally. large teeth which cut the fell emourih For this purpose the novel screw-hep is designed in such a fashion their some toolh-rihgxor even only the first teeth ihereoff, here e smaller fienk diameter While lzeeill with lerger flank diameter are arranged on other teeth-ribs which conform to the diemeeer of she thread to he cut hereinel 'er referred lo es normal *hreed. Preferably e 'lzocih rile' Wicl .orreel thread is always leceted heizweeii iocih ribs with smaller three-d, llie i; sell :eumher sf all the toohh-rihs prefe ly lecing divisible by two. lleturelly this isiicl; ehsolutely necessary. In certain circumstances is even possible to provide enly one HGllfllLl cuisine; rib or even only individual larger teeth offset as desired. The initial out of this screw tsp is so designed their the cull/ii of she eclvence cuts leeih ccril; cl; Wish. e, conical shell surface core centric "with iJl'lB eii'is Wl1ll$i7 ell thc'follcwicg curler ieeih are bounded by e conical shell surface which is also centrally located loui li Wliilllll. ilic cciiicefi shell of the edvence cellihg beech.

The med cs as follows: rence cul leer-c W111i} smaller fienl discrete erige "e Well even in smaller loo-re since i; ey elcne ccme into operation iiiiiielly, Alter e sli hi; depth 01: the l groove has been rough cur, the following c1 medielclr into operelzioii, The latter commence hy placing the fie-like lshe holders of ihe lvhreed groove. The seller hehely errer) gerl '5] errors advance cutting teeth now out steedilydeepcr while the Wide seetli follow slowly in the depth. "Elms File serie effect is achieved as if e lergelollowing cs her were preceded by as small advance cutter. Moreover there is the edvcetege thee ihese screw taps may he designed with very short cut commencing ends, so the; they may oflen These screw taps are naturally particu larly adapted for larger diameters wherewith very many cutting ribs may be provided. In this case the part of the following cutter ribs not cutting at the commencement is best deeply milled away at the front-end of the screw tap in order to create an advantageous shavings space for the advance cutting teeth. If there are only four cutting rows, it is to be recommended that two oppositely located advance cutting rows should be provided,

. 2 while the part of the following cutting ribs not cutting initially conforms as to their outer diameter as precisely as possible to the bore hole diameter. Said part then undertakes the guidance of the screw tap in the hole axis and ensures that the screw tap does not catch, with the two remaining advance cutter rows,

into the material nor the screw vary in rofile.

In order that these ide ribs shall a so not cut the bore askew ue to their sharp edges if the screw tap is applied obliquely, these sharp edges may be broken so that such screw taps are guided in centrally of the bore hole axis under all circumstances, even if cutting is commenced obliquely.

Naturally also two and three cutters may be so designed that the cutting rib with the normal teeth is made at the commencement as a guide rib. Even if the bore hole already has thecorrect dimensions and need not first be cut by the screw tap the idea of constructing certain cutting ribs as guide ribs may also be employed for the design of screw taps with only one cutting rib. This is of importance with smaller screw taps for the purpose of creating a large space for shavings If the radius of this guide rib increases slowly then the bore hole may be made less than core dimension. To increase the adherence to the dimension the guide rib may be provided with normal thread in the last threads.

The advance cutting teeth may conform in flank angle to the following cutters; different angles may, however, also be selected. Different angles are of importance particularly in the case of uare threads, round threads and so forth. e advance cutting teeth may have the same flank diameter or may be disposed at gradually increasing distances from the axis; also the advance cutting teeth may than the theoretical core dimension.

be desi ned with gradually decreasing distances rom the axis in order that they shall not bind in the advance cut groove.

The present method of producing threads is referred to in the specification only in connection with screw taps; reversed, however, it applies also to tools for the production of external threads, such as cutting files, cutting dies and so forth. I

Fig. 1 illustrates the cut profile in diagrammatic representation. This illustration is imagined as if all the rows of teeth of a screw tap were moved in the direction of the thread towards one another in such a fashion that they are combined in one row of teeth. Naturally this is possible only in imagination. All the teeth of the advance cutting portion then lie within the profile of the'following cutting row. The line a a, represents the line bounding the core of the advance cutting row of teeth While the line b 6 indicates the line bounding the core of the following cutting teeth. Thus the core diameter oftheadvance cutting rows is shown smaller than the core diameter of the following cutting rows by the amount 0. As to the outer diameter the advance cutting teeth are bounded in the initial cutting part by the surface (1, a of a cone while the following cutting teeth are bounded by the surface e f of a cone which lies back axially by a distance f a relatively to the conical bounding surface of the advance cutting teeth. The line b I), therefore, bounds the core diameter of the finished thread. Due to the smaller advance cutting teeth, which alone cut at the start, this screw tap will still engage in a bore hole which is smaller by the amount a The advance cutting teeth out the central part of the thread groove as indicated by vertical shading while the following cutting teeth plane the flanks as illustrated by horizontal shading. The core material to be peeled off is carried away by the portion 9, f, constructed like a reamer, of the following cutting rib (cross shading). The part 'f a of the following cutting tooth-ribs may be designed as a non-cutting guide portion, which is formed advantageously in the case of screw ta s with a few rows of teeth only.

igs. 2 and 3 illustrate a practical embodiment by way of example of a screw tap with six cutting ribs. Fig. 2 is a section and Fig. 3 is. an end view in the direction h of the screw tap according to Fig. 2. The toothrows 1, 3 and 5 are the advance cutting rows with a smaller flank diameter. The tooth rows 2, 4 and 6 are the tooth rows with normal teeth. While now the advance cutting tooth-ribs commence at the front end of the screw ta the increase in the tooth height of the fo lowin cutting tooth-ribs only commences at g. be part 9 f of the following cutting tooth-ribs is made, in this example lit like a reamer while portions k of the noncutting forward part ofthe said following cutting tpoth ribs, from f onwards, are deeply milled. oif in order to create a better clearing,

' space for the cuttings from the advance cutting teeth. As shown by the example in Fig. 2 the angle of cut ,6 of the following cutting tooth ribs may be the same as that of the advance cutting tooth ribs. The angle may, however, also be made larger, as for 1nstance the angle a or smaller. The advance cutting tooth ribs 1, 3 and 5 consequently rough cut the hole of the bore smaller than the theoretical core dimension, the reamerlike section gf of the following cutting toothribs cuts out the core peaks and the other following cutting teeth then alternating with the advance cutting teeth finish the. profile of the thread. By this manner of working the smaller screw tap necessary with smaller bore-holes at the same time as a normally large screw tap, half oi the work'- ing time is saved, as compared with the arrangement in series with a stepped screw tap a considerable saving of initial cutting length is achieved;

Figs. 4: and 5 illustrate the enampleoi a screw tap withfour ribs of cutting teeth out which 1 and 3 are the finishing cutting tooth ribs and 2 and 4 the initial cutting tooth ribs.

The initial cutting tooth-ribs commence at the tip of the screw tap. The following cutting tooth-ribs are set bash from the top. The front part of the latter is constructed as a guide rib which may he rounded at i in order to guide more easily.

The action is thenrthe same as with the screw tap of Figs. 2 and 3. With this screw tap also it is generally preferable tor advance cutting tooth-rihs 2 and to enlarge gradually in flank diameter. The advance cutting tooth-ribs 2' and may also he on tended by a short amount in order to ohtoin guide ribs of the diameter oi the guide rihs oi the following cutting ribs.

l claim: I

in A screw cutting tool'cornprising advance I cutters and finishing cutters formed on hit I being formed on different core diameters, the

'ierent core diameters, the leading and oi the tool having advance cutters only and the intermediate portion having advance cutters and finishing cutters which mutilated so that their cutting edges are hounded hy lines which will generate cones in a revolution, the cone of the advance cutters being die, laced axially relatively to thecone of the finishing cutters.

2. A screw cutting tool comprising a pin-- rality of cutter rubs-certain of said ri'hs having advance cutters and the remainder having finishing cutters, the respective cutters advance cutters only extending to the leading end of the tool, said advance cutters and finishing cutters being mutilated in the interadvance cutters being displaced axially relatively to the cone of the finishing cutters.

3. Screw cutting tool comprising advance cutter teeth and finishing cutter teeth of sim ilar formation and depth, these respective cutter teeth being formed on cores of different diameter the core diameter of the ad Vance cutter teeth increasing from the leading end rearwardlyso that the advance cut,- ter teeth are disposed at gradually increas-' ing distances from the axis, the edges of mutilated finishing cutter teeth in an intermediate portion of the tool being contained in a cone which lies back from the leading end of the tool and is rearwardly spaced from a cone containing the edges of mutilated advance cutter teeth which alone extend over said intermediate and leading end portions.

4(A screw cutting tool comprising a plurality of cutter ribs certain of the said ribshaving advance cutters and the remainder having finishing cutters, the respective cutters lacing termed on different core diameters, the leading and oi? the tool having advance cutonly, said advance cutters and finishing cutters being mutilated in the intermediate portions hetween the leading and rear end portions of the tool so that their cutting edges are bounded by lines which will generate cones in a revolution, the cone of the advance cutters being displaced axially reletively to the cone oi. the finishing cutters, the finishing teeth rihs being formed as reaincrs point immediately hehind the first advance teeth. Y

A. mrew cutting tool comprising a plurality of cutter ribs certain of the said rihs having advance cutters and the. remainder having finishing cutters, the respective out being formed on difierent core die 1.."

eters, the leading end oi the tool having edlid Vance cutters only, said advance cutters and finishing cutters being mutilated in. the interm-edicts portions between the leading and rear end ortions oi the tool so that their cutting e gee are bounded by lines which will generate cones in a revolution, the cone oi the advance cutters being displaced axially relatively to the cone oi the finishing cu tors, tool guiding means being iformed by thenonmutting end portions offinishmg cuttar rihs, corresponding end portions of advanccd cutter ribs heing efiective for initial cutting. v

it. screw cutting rahty of cutter ribs certain 0 he said ribs having advance ,.c utters and the remainder having finishingj ii utters, the respective cutters being formed on different core diameters, the leading end of the tool having advance cutters only, said advance cutters and tool comfprising a plufinishing cutters being mutilated the intermediate portions between the leading and rear end wrt'ons of the tool so that their cutting e ges are bounded by lines which will generate cones in a revolution, the cone ,of the advance cutters being displaced axially relatively to the cone of the fimshing cutters, clearing space for cuttin cutting teeth being provi ed by deeply milled ofi gortions of the non-cutting forward part of t e ribs of the finishing cutters.

v HERMANN STEINRUCK.

from the advance 

